1. Field of the Invention
The present invention relates to a vibration generator used for a vibrating pile driver, various shakers, sieving equipment, and the like and, more particularly, to the vibration generator capable of obtaining an arbitrarily and infinitely changeable vibromotive force or amplitude by rotating eccentric weights.
2. Description to the Prior Art
As the vibration generator utilizing the centrifugal force which is generated by rotating eccentric weights, there is known a vibration generator in which even numbers of a pair of rotational shafts with eccentric weights are rotatively supported in a casing member in parallel with each other and at the same time, driving gears are mounted on each of the rotational shafts to allow the adjacent gears to engage each other, so that one group of the rotational shafts and the other group thereof are rotated in the opposite directions to offset the horizontal components of the centrifugal force generated by the eccentric weights mounted on each of the rotational shafts and to add the vertical components simultaneously; thus providing the casing member with the vibromotive force by the aforesaid vertical components in the vertical direction, for example.
In a vibration generator such as this, the entire body of the vibration generator is vibrated with frequency in response to the revolution of the rotational shaft by means of supporting the casing member through springs or dampers. As a result, it is possible to drive in the pile or draw it out by actuating the vibration generator while supporting a pile such as a steel sheet pile with the casing member through a chuck, and it is also possible to perform mixing work or sieving work by incorporating such vibrating generator with a shaker or sieving equipment.
In the conventional vibration generator mentioned above, the eccentric weights are fixed to the rotational shafts, thus making it difficult to modify the vibromotive force or amplitude arbitrarily during operation. Furthermore, in a vibration generator such as this, the driving power required to rotate the eccentric weights at rest at the initial stage of the operation is extremely large as compared with the driving power required to rotate the weights which have once arrived at the rated revolution thereof. Accordingly, if the driving power required to rotate the eccentric weights at rest before bringing them to the rated revolution could be reduced, it should be possible to implement the miniaturization of the driving power source such as a motor, thereby improving significantly the utilization efficiency of energy such as power to be consumed. Therefore, there is a strong demand that a method should be implemented thereby to reduce with ease the driving power required for the revolution of the rotational shafts at the initial stage of the operation.
Also, in the vibration generator used for a vibrating pile driver, for example, it is required to implement a method thereby to modify with ease the vibromotive force or amplitude in response to the ground condition and the like at a location where the pile is driven in so as to improve the operativity of the pile driving or that of the pile drawing, or a method thereby to prevent the resonance phenomena generated at the time of activating or braking the vibration.
To meet such demands as mentioned above, several vibration generators capable of modifying the vibromotive force or amplitude are in consideration at present. However, there exists a disadvantage in all of them that the number of parts is great due to the complicated structure, leading unavoidably to a significant cost increase.
In consideration of these problems, the object of the present invention is to provide a vibration generator capable of varying the vibromotive force or amplitude arbitrarily and infinitely even during the operation, which is yet simply and rationally structured so as to be built with ease.